The winger's goal did more than just take the roof off Celtic Park; it secured the club a financial bounty of at least £15million for the second successive season, while also helping to lift Scotland's battered coefficient.
It is on the park, though, where the ramifications of his last-gasp winner will really be felt. He has set Celtic up with a programme of intrigue between now and Christmas as they attempt to punch above their weight once more against the heavyweights of European football.
Barcelona, AC Milan and Ajax might be becoming familiar opponents for Celtic in this tournament, but there is no question they are formidable company for Lennon's men in Group H.
And if Celtic are to do anything at all in this competition then they will need the influential members of the team to relish the company they are in.
None more so than Forrest. The Scotland internationalist has been struggling for the past 10 months or so with a catalogue of injuries, prompting Lennon to reveal last week the club were consulting a neurologist in order to try to get to the root of his problems.
Since then Forrest's sciatic nerve issues appear to have eased off, but Lennon would love nothing more than to have the player notch up a run of games that would see him get back to his best.
There has been a few murmurs of frustration from supporters that the player hasn't reached the heights he did a few seasons back when he won the PFA Young Player of the Year award - but Lennon was nothing but fulsome in his praise and defence of the winger.
"It's rubbish," said Lennon. "He wants to play but it has not always been possible for him as he has been ravaged with injuries. It's sad sometimes, it's like watching a thoroughbred lame.
"When he plays and when he's in full flow we don't have many better than him. One run in particular the other night was fabulous when he came in off the left-hand side and went right across the box.
"He's brave, he always wants to take the ball, he tries to make something happen and I couldn't have been more pleased for him when he scored the goal. He'd taken a heavy dunt and he was feeling it, so in more ways than one he's brave.
"I think he's a brilliant player, I really do. He totally vindicated my selection."
And the Northern Irishman believes that some of the flak that has been directed towards Forrest has been nonsense, especially when consideration is given to the fact that he has been playing with an injury.
"I'd love him to have a 15 or 20-game run where he is injury-free because you'd really see the best of him then as he is a talent," said the Celtic boss.
"We see it every day, we know what he can do, he's the type of player who can get you off your seat.
"I don't know what people want from him. There are times when he's got three hanging off him and he still seems to get away from them.
"I don't know if they expect him to do that all the time, it's impossible to do that. But for what he's done in his career so far I think he's had a fabulous start to his career.
"I think there is far more to come from him as well. I think he's one of the most naturally gifted footballers to come out of the country in a long time."
Meanwhile, Lennon is optimistic that Israeli midfielder Nir Biton can help to fill the void that has been left in Victor Wanyama's absence - however, he was quick to insist that his arrival did not signal anything significant about Beram Kayal.
Biton yesterday agreed a deal with the club and he will feature in the squad for this afternoon's game at Tannadice.
"He's a class player, he's tall, good engine, he's got soft feet, he's got a good range of passing and he's powerful when he gets going," said Lennon.
"What he will bring is a bit of extra quality to the midfield because we have been a little bit light there since Victor left.
"He takes it in and he's got a good feel for the ball.
"There are no implications for Beram. Biton can do both, he can be a box-to-box player as well.
"I've seen him play both positions, more as an attacking midfielder for his club, and for his country I've seen him play in a defensive role.
"We have liked him for over a year now. I thought he was very good in the Under-21 Championship in the summer. That wasn't the reason why he caught our eye, we've known about him for a long time. He's come from the same club as Efe Ambrose, so we knew about him even then."
While Lennon's focus will be taken up today by the game against Dundee United, his phone is liable to be red-hot as he seeks to do a bit more business before the transfer window closes.
However, he is baffled as to why the window closes earlier in Scotland than elsewhere.
" I don't know why that is but it doesn't make it any easier," he said.
"I'll be glad when it closes because there it is, there's your squad to work with - no-one's leaving, no-one's coming in and we can get on with it. It drives you crackers sometimes.
"You sometimes go boom, boom, boom, boom, boom - make four or five deals in one day and that is really not what you want to do.
"In the old days you could say, 'Well, I could do with a player come December and we'll bring this one in' to replace an injured player. That was a lot easier for managers.
"But we know what the stipulations are and try to work within them as best we can."